Since the public beta release of Ribbit Phone's VoIP web services, it is now really easy to add voice over IP capabilities to any Flex application.

This tutorial goes through the process of getting started and shows how little code is necessary to get going. The code sample in this tutorial will be able to phone a telephone number from Flex using your computer’s microphone and speakers.

This tutorial demonstrates how to upload a local file to a remote web server using Flex and PHP. Flex provides the UI for a user to choose a file and then sends that data to a PHP script on the server side to do the processing.

Learn how to build a Flex application that accesses your Facebook photos.

This tutorial continues on the process put forth in the first Facebook tutorial Building Facebook Applications with Flex.

After following the steps laid out in the first tutorial, all you will need to do is add a few lines of code to the MXML file.

Since the public release of the Facebook API there has been a huge rush of developers building Facebook applications. There are official PHP and Java libraries available via the developer resources pages, but no official ActionScript library as of this writing. Tim Whitman has created a great (unofficial) ActionScript 2 library for people developing in Flash.

Flex 2 has difficulties loading SWFs that aren't published as ActionScript 3. 

If you want to load Flash movies that are published as ActionScript 2 into your Flex project you can use an SWFLoader. However, if you want to call ActionScript commands on that loaded file you need to communicate using a LocalConnection.

Peter Ent has a thorough explanation of this process here.